This invention relates to a passive remote head for a photoelectric detection and counting apparatus wherein the head is remote from any power source and thus can be used under many conditions where a power source may be dangerous.
Available photoelectric counting devices generally include a sensor head having a light source and a light detection device. In the prior art, the power source and/or the source of light itself must be within the head or within 5 or 6 feet of the head in order to obtain a useful effect. When using the sensor device under conditions such as the presence of highly combustible or explosive gases or other materials, the presence of a power source intrinsically reduces the safety of the system.
Previously available photoelectric detection and counting devices include a photo-sensor and a light emitting device directed towards, for example, a continuous flow of objects on a conveyor which are to be monitored, for example, for the purpose of counting the objects and to determine that a given number pass within a given time period. In this exemplary application, as one after the other of the objects to be detected by the sensor passes in front of the sensor head, the objects to be detected break the light beam being directed back to the element in the head.
Depending upon the material to be detected and counted, the counter can be based upon a continuous stream of light from the light source to a reflector element and back to the sensor element in the head, which is broken by a passing object; alternatively, the continuous beam of light can be reflected by the object to be counted, thereby impinging upon the sensor element in the head. In either case, the source of the light has previously been either in the head or in a power source within, usually, 5 or 6 feet of the head. Such a power source, e.g., electricity, can of course be a significant problem when the environment is filled with a highly combustible or explosive gas or vapor, such as volatile hydrocarbons, or hydrogen gas. Such photoelectric devices can also be useful for the detection of the movement of a machine part from one position to a second predetermined position, as well as many other applications involving the movement of solid objects.
Sensors for such photoelectric devices are of two general types: in the first, a single housing contains both the light emitter and the receiver and a reflecting target is used to rebound the beam from the emitter back to the receiver, across the path of the objects to be detected. The second type uses an emitter and a receiver in separate and opposed housings, which are placed on opposite sides of the path of the objects to be detected, with a beam being transmitted directly from the emitter across that path to the receiver. The first type of sensing system of course is more compact, which at times becomes critical to the application to which the sensor is to be put. It is further desirable, especially in a situation where the sensor head is located at a distance from any control means, that the optical system be extremely tolerant of the distance between the lens and the object to be measured, or the reflecting surface.